Method of manufacturing semiconductor device

ABSTRACT

In a method of manufacturing a semiconductor device, a first heat treatment for crystallization is conducted after nickel elements are introduced in an amorphous silicon film. Then, after the crystalline silicon film is obtained, a heat treatment is again conducted through the heating method which is identical with the first heat treatment. In this state, HCl or the like is added to the atmosphere to conduct gettering of the nickel elements remaining in the crystalline silicon film. With this process, there can be obtained a crystalline silicon film low in the concentration of the metal elements and high in crystallinity.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of manufacturing asemiconductor device represented by a thin-film transistor. Moreparticularly, the present invention relates to a method of manufacturinga semiconductor device using a silicon thin film having crystallinitywhich is formed on a glass substrate or a quartz substrate.

[0003] 2. Description of the Related Art

[0004] Up to now, there have been known thin-film transistors using asilicon film. The thin-film transistor is structured using a siliconfilm (several hundreds to several thousands Å in thickness) formed on aglass substrate or a quartz substrate.

[0005] The reason why the glass substrate or the quartz substrate isused is to employ the thin-film transistor for an active matrixliquid-crystal display unit.

[0006] Under existing circumstances, in the case of using the glasssubstrate, a general technique is that the thin-film transistor isformed using the amorphous silicon film. In the case of using the quartzsubstrate, a technique in which the crystalline silicon film obtainedthrough a heat treatment is used has been put to practical use.

[0007] Compared with the thin-film transistor using the amorphoussilicon film, the thin-film transistor using a crystalline silicon filmenables high-speed operation of two digits or more to be performed.Hence, a peripheral drive circuit of the active matrix liquid-crystaldisplay unit, which has been conventionally made up of an IC circuitexternally attached hereto can be formed of a thin-film transistor onthe glass substrate or the quartz substrate.

[0008] The above structure is very advantageous in the downsizing of theoverall device or simplification of a manufacturing process. Also, thestructure leads to reduction of the manufacturing costs.

[0009] As a technique by which a crystalline silicon film is obtainedthrough a heating treatment, there has been known a technique disclosedin Japanese Patent Unexamined Publication No. Hei 6-232069. According tothe technique, a metal element (for example, nickel) that promotes thecrystallization of silicon is introduced into an amorphous silicon filmso that the crystalline silicon film is obtained through a heattreatment at a lower temperature than a conventional one.

[0010] Using that technique, an inexpensive glass substrate as can beused as a substrate, and the crystalline silicon film as obtained canprovide crystallinity which can be practically used over a wide area.

[0011] However, because the metal element is contained in the film andthe control of its introduced amount is subtle, it is proved that therearise problems on the reproducibility and the stability (electricstability of the obtained device).

SUMMARY OF THE INVENTION

[0012] The present invention has been made in view of the abovecircumstances, and therefore an object of the present invention is toprovide a technique by which the concentration of metal elements in acrystalline silicon film obtained by using metal elements that promotethe crystallization of silicon is lowered.

[0013] In order to solve the above problem, according to one aspect ofthe present invention, there is provided a method of manufacturing asemiconductor device, comprising the steps of: intentionally introducingmetal elements that promote crystallization of silicon in an amorphoussilicon film to crystalize said amorphous silicon film through a firstheat treatment; and conducting a second heat treatment in an atmospherecontaining halogen elements therein to intentionally remove said metalelements; wherein said first heat treatment and said second heattreatment are conducted by identical heating means.

[0014] In the above method, it is important that the first heattreatment and the second heat treatment are conducted by the identicalheating means. This is because in the case where the first heattreatment for diffusing the metal elements in the silicon film toconduct crystallization and the second heat treatment for removing themetal elements diffused in the silicon film are conducted through anidentical method, the removal of the metal elements is carried out moreeffectively.

[0015] For example, in the case of using nickel as the metal elements,conducting the first heat treatment through a heating by a heater, andconducting the second heat treatment through heating by an infrared raylamp (RTA: rapid thermal annealing), it is proved that the effect ofremoving nickel from the silicon film is lower than that in the case ofusing the heater in both of the heating methods.

[0016] According to another aspect of the present invention, there isprovided a method of manufacturing a semiconductor device, comprisingthe steps of: holding metal elements that promote crystallization ofsilicon in contact with a front surface or a rear surface of anamorphous silicon film; conducting a first heat treatment on saidamorphous silicon film to crystallize at least a part of said amorphoussilicon film; and conducting a second heat treatment in an atmospherecontaining halogen elements on the silicon film to intentionally removesaid metal elements, wherein the first heat treatment and the secondheat treatment are conducted by the identical heating means.

[0017] As metal elements that promote crystallization of silicon, therecan be used one kind or a plurality of kinds selected from Fe, Co, Ni,Ru, Rh, Pd, Os, Ir, Pt, Cu and Au.

[0018] In particular, the use of Ni (nickel) is most preferable from theviewpoint of its effect and reproducibility.

[0019] As an atmosphere containing halogen elements therein, there canbe used one kind of gas or a plurality of kinds of gases selected fromHCl, HF, HBr, Cl₂, F₂ and Br₂ being added to the atmosphere containingone kind of gas or a plurality of gases selected from Ar, N₂, He and Ne.In this example, halogen elements function to remove the metal elements.

[0020] Also, as an atmosphere containing halogen elements therein, therecan be used oxygen and one kind of gas or a plurality of kinds of gasesselected from HC;, HF, HBr, Cl₂, F₂ and Br₂ being added to theatmosphere containing one kind of gas or a plurality of gases selectedfrom Ar, N₂, He and Ne.

[0021] Oxygen has a function to suppress the surface of the silicon filmfrom being roughened by action of halogen elements since oxygen formsthe oxide film on the surface of the silicon film simultaneously duringthe process of removing the metal elements.

[0022] The heat treatment for removing the metal elements can beconducted at a temperature of 450 to 1050° C.

[0023] With intentional introduction of the metal elements representedby nickel, the amorphous silicon film is crystallized through the firstheat treatment. Then, the second heat treatment is conducted in theatmosphere containing halogen elements, to thereby remove the metalelements intentionally introduced from the film. In this situation, thefirst heat treatment and the second heat treatment may be conducted bythe identical means.

[0024] The above and other objects and features of the present inventionwill be more apparent from the following description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIGS. 1A to 1D are diagrams showing a process of obtaining acrystalline silicon film;

[0026]FIGS. 2A to 2D are diagrams showing a process of obtaining acrystalline silicon film;

[0027]FIGS. 3A to 3E are diagrams showing a process of manufacturing athin-film transistor;

[0028]FIGS. 4A to 4E are diagrams showing a process of manufacturing athin-film transistor; and

[0029]FIGS. 5A to 5F are diagrams showing a process of manufacturing athin-film transistor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Now, a description will be given of preferred embodiments of thepresent invention with reference to the accompanying drawings.

[0031] (First Embodiment)

[0032] A first embodiment of the present invention exhibits a techniquein which a crystalline silicon film is formed on a glass substrate usingnickel elements.

[0033]FIGS. 1A to 1D show a manufacturing process in accordance withthis embodiment of the present invention. First, a silicon oxynitridefilm 102 is formed in thickness of 3000 Å on a Corning 1737 glasssubstrate (strain point of 667° C.) 101 as an under layer.

[0034] The formation of the silicon oxynitride film is conducted throughthe plasma CVD method using silane, N₂O gas and oxygen as a raw gas.Alternatively, the formation is conducted through the plasma CVD methodusing TEOS gas and N₂O gas.

[0035] The silicon oxynitride film functions to prevent impurities (theglass substrate contains a large amount of impurities from the viewpointof a level in manufacturing a semiconductor device) from being diffusedfrom the glass substrate during the post-process.

[0036] It should be noted that a silicon nitride film is optimum inobtaining that function at maximum. However, since the silicon nitrideis separated from the glass substrate due to a stress, it is notpractically used. Also, a silicon oxide film may be used as the underfilm. However, the silicon oxide film has an insufficient barrier effectwith respect to the impurities in comparison with the silicon oxynitridefilm.

[0037] It is important that the under layer has the hardness as high aspossible. This is concluded from the fact that in the endurance test ofthe thin-film transistor as finally obtained, the harder under layer(that is, the under layer smaller in its etching rate) is higher inreliability. Also, it is presumed from that conclusion that the hardnessof the under film is relevant to the prevention of the impurities'entering from the glass substrate.

[0038] Then, an amorphous silicon film 103 which will be formed into acrystalline silicon film is formed in thickness of 500 Å through the lowpressure thermal CVD method. The reason why the low pressure thermal CVDmethod is used is that the quality of the crystalline silicon film whichwill be obtained later is excellent. It should be noted that the plasmaCVD method can be used as a method other than the low pressure thermalCVD method.

[0039] It is preferable that the thickness of the amorphous silicon film103 is set to 2000 Å or less. This is because in a stage where metalelements that promote the crystallization of silicon are removed, if itsthickness is set to 2000 Å or more, its removal becomes difficult.

[0040] Also, the lower limit of the thickness of the amorphous siliconfilm 103 is determined by how thin the film can be formed in the filmformation. In general, about 100 to 200 Å is its lower limit.

[0041] Also, it is important that the impurities are prevented frommixedly entering the film with the greatest care. Specifically, it isimportant that attention is paid to the purity of gas used for forming afilm and cleaning of the device. In the above manner, a state shown inFIG. 1A is obtained.

[0042] Subsequently, a nickel acetate solution containing nickelelements therein of 10 ppm (weight conversion) is coated on the surfaceof the amorphous silicon film 103.

[0043] Specifically, as shown in FIG. 1B, a water film 104 of the nickelacetate solution is formed on the surface of the amorphous silicon film103. Then, an excessive solution of the nickel acetate solution is blownoff using a spin coater. That is, spin drying is conducted.

[0044] With the above process, there is obtained a state in which thenickel elements are held in contact with the surface of the amorphoussilicon film 103.

[0045] It should be noted that from the viewpoint of the remainingimpurities in the following heating process, it is preferable to usenickel sulfate instead of nickel acetate solution. This is becausenickel acetate solution contains carbon, and the carbon may becarbonized during the subsequent heating process and remain in the film.

[0046] The adjustment of the amount of introduced nickel elements can beconducted by adjusting the concentration of the nickel elements in thesolution. Also, the amount of introduced nickel elements can becontrolled in accordance with a condition under which spin drying isconducted and a holding time of the solution on the amorphous siliconfilm 103.

[0047] Then, in a state shown in FIG. 1C, a heat treatment is conductedat a temperature of 450 to 650° C. to crystallize the amorphous siliconfilm 103.

[0048] In this step, the heat treatment is conducted at 600° C. in thenitrogen atmosphere for four hours. As a result of this process, acrystalline silicon film 105 is obtained.

[0049] It is important that the upper limit of heating temperature inthe heat treatment is determined in accordance with the heat resistanceof the substrate to be used. In this embodiment, since the Corning 1737glass substrate whose strain point is 667° C. is used, the condition ofthe heating temperature is about 650° C. Also, it is proved byexperiments that the heating temperature of 450° C. or higher isrequired for crystallization.

[0050] Furthermore, in the case of using a quartz substrate or anothermaterial high in heat resistance as a substrate, the heating temperaturefor the above crystallization can be further increased. For example, inthe case of using the quartz substrate, the heating temperature can beincreased up to about 1000° C.

[0051] The increase in the temperature leads to such advantages that aperiod required for the heat treatment can be shortened, and also highercrystallinity can be obtained.

[0052] In the above crystallization process, the nickel elements whichhave been held in contact with the surface of the amorphous silicon film103 are dispersed in the film. Then, this largely contributes to thecrystallization of the amorphous silicon film 103.

[0053] Subsequently, as shown in FIG. 1D, a heat process for removingthe nickel elements that have remained in the crystalline silicon film105 and have been used for crystallization is conducted. The heattreatment is conducted at a temperature of 600° C. in the nitrogenatmosphere containing halogen elements.

[0054] In this example, the heat treatment is conducted at 600° C. for10 minutes in the atmosphere where 3% of HCl is added to the nitrogenatmosphere.

[0055] The concentration of HCl in the atmosphere is preferably set to 1to 10%. If the concentration is set to a value more than that range,attention must be paid because the surface of the silicon film isroughened. If the concentration is set to a value less than that range,the gettering effect is lowered.

[0056] Further, it is effective to add oxygen to the atmosphere underwhich the above heat treatment is conducted. In this case, the roughsurface of the silicon film due to the halogen elements is flattened bythe formation of the oxide film. The amount of addition of oxygen may beadjusted so that the concentration of oxygen in the atmosphere becomes20 to 50%.

[0057] Also, the lower limit of the above heat treatment temperature ispreferably set to 450° C. or higher from the viewpoint of its effect andreproducibility. Also, it is important that its upper limit is set tothe strain point of the glass substrate 101 to be used or less.

[0058] Hence, the use of the quartz substrate enables the heatingtemperature to further increase up to about 1000° C. In this case, theeffect of removing the nickel elements can be further enhanced. Also,the processing period can be shortened.

[0059] However, since the etching effect on the silicon film isremarkable, it is required that the concentration of the halogenelements is lowered, and that oxygen is added thereto.

[0060] A gas which is generally called “inactive gas” can be used otherthan the nitrogen atmosphere. In particular, one kind or a plurality ofgases selected from Ar, He and Ne can be used.

[0061] As a gas for introducing the halogen elements, one kind or aplurality of gases selected from HF, HBr, Cl₂, F₂, Br₂, and NF_(3,) ClF₃can be used other than HCl. It is preferable that the content (volumecontent) of the gas in the atmosphere are set to 0.3 to 10% if it is HF,1 to 20% if it is HBr, 0.3 to 5% if it is Cl₂, 1 to 3% if it is F₂, and0.3 to 10% if it is Br₂.

[0062] By the heat treatment which has been again conducted in the aboveatmosphere containing the halogen elements as described above, theconcentration of the nickel elements can be set to {fraction (1/10)} ofan initial concentration, or less. This means that the nickel elementscan be set to {fraction (1/10)} or less in comparison with a case inwhich gettering due to the halogen elements is not conducted. The effectis obtained similarly in the case of using other metal elements.

[0063] For example, in the crystalline silicon film which has beencrystallized through the heat treatment in the nitrogen atmosphere usingthe nickel elements, the nickel elements have been observed at aconcentration of about 1×10¹⁹ to 5×10¹⁹ cm⁻³ through the measurement ofSIMS (secondary ion mass spectrometry).

[0064] On the contrary, in the case of applying this embodiment, theconcentration of detected nickel is about 1×10¹⁸ to 5×10¹⁸ cm⁻³. Ofcourse, it is presumed that the condition under which nickel isintroduced is identical.

[0065] It should be noted that in this embodiment, there is shown anexample in which solution is used to introduce nickel elements from theviewpoints of the excellent controllability and simpleness. However,there may be used a method of forming nickel or a film containing nickelthrough the CVD method or the sputtering method. Also, there may be useda method of holding the nickel elements in contact with surface of theamorphous silicon film through the adsorption method.

[0066] Likewise, this is applied to a case of using other metal elementsthat promote the crystallization of silicon.

[0067] (Second Embodiment)

[0068] A second embodiment of the present invention relates to anexample of conducting the crystal growth different in form from thefirst embodiment. This embodiment relates to a method of conductingcrystal growth in a direction parallel to a substrate, which is called“lateral growth”, using metal elements that promote the crystallizationof silicon.

[0069]FIGS. 2A to 2D show a manufacturing process in accordance withthis embodiment. First, a silicon oxynitride film 202 is formed inthickness of 3000 Å on a Corning 1737 glass substrate (it may be aquartz substrate) as an under layer.

[0070] An amorphous silicon film 203 is formed in thickness of 500 Åthrough the low pressure thermal CVD method.

[0071] Then, a silicon oxide film not shown is formed in thickness of1500 Å, and then patterned to form a mask indicated by reference numeral204. An opening is formed on the mask in a region indicated by 205, andthe amorphous silicon film 203 which is an under layer is exposed atthat region.

[0072] The opening 205 has a slender rectangle which extendlongitudinally depthwise of the drawing. The width of the opening 205may be set to 20 μm or more. The length in the longitudinal directionmay be arbitrarily determined.

[0073] The nickel acetate solution containing the nickel elements of 10ppm in weight conversion shown in the first embodiment is coatedthereon. Then, an excessive solution is blown off using a spin coater.

[0074] In the above manner, as indicated by a dotted line 206, thenickel elements are held in contact with the exposed surface of theamorphous silicon film 203 and the surface of the mask 204 which is thesilicon oxide film (FIG. 2A).

[0075] Subsequently, a heat treatment is conducted at 600° C. for 4hours in the nitrogen atmosphere containing no oxygen as much aspossible. With this process, crystal growth in parallel with thesubstrate is progressed as indicated by reference numeral 207 in FIG.2B. The crystal growth is progressed from the region of the opening 205into which the nickel elements have been introduced toward theperiphery. The crystal growth directed in parallel with the substrate iscalled “lateral growth”.

[0076] The lateral growth can be conducted over 100 μm or more. Asilicon film 208 thus having the lateral region is obtained (FIG. 2B).

[0077] Then, the mask 204 which is the silicon oxide film forselectively introducing the nickel elements is removed to obtain a stateshown in FIG. 2C. In this state, the lateral growth region and a region(having an amorphous silicon state) which is not subjected to crystalgrowth exist in the silicon film 208.

[0078] Then, in this state, a heating treatment is conducted at 600° C.for 10 minutes in the atmosphere comprising 5% of HCl, 5% of oxygen and90% of nitrogen.

[0079] With this process, as described in the first embodiment, theconcentration of the nickel elements in the film can be reduced.

[0080] Subsequently, a pattern 209 which is the lateral growth region isformed by patterning. In this example, it is important that the pattern209 is designed such that a start point and an end point of the crystalgrowth do not exist in the pattern 209.

[0081] This is because the nickel elements of a relatively highconcentration are contained in the start point and the end point of thecrystal growth.

[0082] The concentration of the nickel elements remaining in the pattern209 thus obtained which is the lateral growth region can be set to befurther lower compared with the case of the first embodiment.

[0083] This is also because the concentration of the metal elementscontained in the lateral growth region is originally low. Specifically,the concentration of the nickel elements in the pattern 209 which is thelateral growth region can be set to the order of 10¹⁷ cm⁻³.

[0084] Also, the device is designed in such a manner that the lateralgrowth direction and the carrier moving direction are substantiallyidentical with each other, thereby being capable of obtaining the devicehaving a higher mobility compared with the case of using the crystalgrowth method shown in the first embodiment.

[0085] (Third Embodiment)

[0086] A third embodiment of the present invention exhibits an exampleof manufacturing a thin-film transistor disposed in a pixel region of anactive matrix type liquid-crystal display unit or an active matrix typeEL display unit.

[0087]FIGS. 3A to 3E show a manufacturing process in accordance withthis embodiment. First, a crystalline silicon film is formed on a glasssubstrate through the process shown in the first embodiment or thesecond embodiment. Then, the crystalline silicon film is patterned toobtain a state shown in FIG. 3A.

[0088] In the state shown in FIG. 3A, reference numeral 301 denotes aglass substrate; 302, an under film; and 303, an active layer formed ofa crystalline silicon film. In this example, it is preferable that theunder film is formed of a silicon oxynitride film. Also, it is desirablethat halogen elements are contained in the silicon oxynitride film. Thisis because the gettering operation of the metal ions and movable ionsdue to halogen elements is used.

[0089] After the state shown in FIG. 3A is obtained, a siliconoxynitride film 304 forming a gate insulation film is formed inthickness of 1000 Å. The film forming method is plasma CVD method usinga mixture gas consisting of oxygen, silane and N₂O, or plasma CVD methodusing a mixture gas consisting of TEOS and N₂O.

[0090] Also, that the halogen elements are contained in the siliconoxynitride film is useful in prevention of the function of the gateinsulation film as an insulation film from being deteriorated by theinfluence of the nickel elements (other metal elements that promote thecrystallization of silicon) which exist in the active layer.

[0091] The formation of the silicon oxynitride film has significance inthat the metal elements are hard to enter in the gate insulation filmdue to its fine quality of the film. If the metal elements enter in thegate insulation film, its function as the insulation film isdeteriorated, causing the instability and the dispersion of thecharacteristics of the thin-film transistor.

[0092] It should be noted that a silicon oxynitride film normally usedcan be used for the gate insulation film.

[0093] After the silicon oxynitride film 304 that functions as the gateinsulation film has been formed, an aluminum film (not shown) which willfunction as a gate electrode later is formed through the sputteringmethod. 0.2 wt % of scandium is contained in the aluminum film.

[0094] The reason why 0.2 wt % of scandium is contained in the aluminumfilm is to suppress occurring of hillock or whisker in the subsequentprocess. Hillock and whisker are directed to a needle-like projectiongenerated by heating. It is considered that the hillock and the whiskerare caused by the abnormal growth of aluminum.

[0095] After the formation of the aluminum film, a dense anodic oxidefilm not shown is formed. The anodic oxide film is formed using anethylene glycol solution containing tartaric acid of 3% as anelectrolyte solution.

[0096] The anodic oxidization is conducted with the aluminum film as ananode and platinum as a cathode in the electrolyte solution, to therebyform the dense anodic oxide film on the surface of the aluminum film.

[0097] The thickness of the dense anodic oxide film not shown is set toabout 100 Å. The anodic oxide film serves to improve the adhesion to aresist mask which will be formed later.

[0098] It should be noted that the thickness of the anodic oxide filmcan be controlled by a supply voltage when anodic oxidizing.

[0099] Thereafter, a resist mask 306 is formed. Then, an aluminum film305 is patterned in a pattern indicated by reference numeral 305. Inthis way, a state shown in FIG. 3B is obtained.

[0100] In this situation, anodic oxidization is again conducted. In thisexample, an oxalic acid aqueous solution of 3% is used as theelectrolyte solution. Anodic oxidization is conducted with the pattern305 of aluminum as the anode in the electrolyte solution, to therebyform a porous anodic oxide film indicated by reference numeral 308.

[0101] In this process, because the resist mask 306 high in adhesionexists in the upper portion, an anodic oxide film 308 is selectivelyformed on the side surfaces of the aluminum pattern.

[0102] The anodic oxide film 308 can grow up to several μm in thickness.In this example, its thickness is set to 6000 Å. It should be noted thatthe growth distance can be controlled by anodic oxidation period.

[0103] Then, a dense anodic oxide film is again formed. In other words,using the above-mentioned ethylene glycol solution containing 3% oftartaric acid as an electrolyte solution, anodic oxidization is againconducted. As a result, because the electrolyte solution enters in theporous anodic oxide film 308, a dense anodic oxide film as indicated byreference numeral 309 is formed. The thickness of the dense anodicoxidation film 309 is set to 1000 Å (FIG. 3C).

[0104] In this example, the exposed portion of the silicon oxynitridefilm 304 is etched. It is useful to utilize the dry etching as thatetching. Further, the porous anodic oxide film 308 is removed by amixture acid consisting of acetic acid, nitric acid and phosphoric acid.In this way, a state shown in FIG. 3D is obtained.

[0105] After the state shown in FIG. 3D is obtained, the implantation ofimpurity ions is conducted. In this example, in order to manufacture then-channel type thin-film transistor, the implantation of P (phosphorus)ions is conducted through the plasma doping method.

[0106] In this process, heavy doped regions 311 and 315 and light dopedregions 312 and 314 are formed, respectively. This is because a part ofthe remaining silicon oxynitride film 310 functions as a translucentmask, and a part of implanted ions is shielded there.

[0107] Thereafter, a laser beam or an intense light is irradiatedthereon, to thereby activate a region in which the impurity ions havebeen implanted. In this way, a source region 311, a channel formationregion 313, a drain region 315, and low-density impurity regions 312 and314 are formed in a self-alignment manner.

[0108] In this example, what is indicated by reference numeral 314 is aregion which is called “LDD (light doped drain) (FIG. 3D).

[0109] It should be noted that in the case where the thickness of thedense anodic oxide film 309 is thickened to 2000 Å or more, thethickness allows an offset gate region to be formed outside of thechannel formation region 313.

[0110] Similarly, in this embodiment, although the offset gate region isformed, since its dimensions are small so that the contribution of theoffset gate region is small, and in order to avoid complicating thedrawing, it is not shown in the figure.

[0111] Thereafter, a silicon oxide film, a silicon nitride film or alaminate film thereof is formed as an interlayer insulation film 316.The interlayer insulation film 316 may be constituted by a layer made ofa resin material on the silicon oxide film or the silicon nitride film.

[0112] Then, contact holes are defined to form a source electrode 317and a drain electrode 318. In this way, a thin-film transistor shown inFIG. 3E is completed.

[0113] (Fourth Embodiment)

[0114] A fourth embodiment of the present invention relates to a methodof forming a gate insulation film 304 in the structure shown in thethird embodiment. In the case of using a quartz substrate or a glasssubstrate high in heat resistance, it is preferable that the thermaloxidation method is used as a method of forming the gate insulationfilm.

[0115] Since the oxide film formed through the thermal oxidation methodis fine (dense) as the insulation film and does not contain chargesinternally movable therein, it is one of optimum gate insulation films.

[0116] As a method of forming the thermal oxide film, there can berecited an example of processing in the oxide atmosphere at atemperature of 950° C.

[0117] In this situation, it is effective to mix HCl or the like in theoxide atmosphere. With this process, the metal elements that exist inthe active layer can be removed while the thermal oxide film is beingformed.

[0118] Also, it is effective that N₂O gas is mixed in the oxideatmosphere to form a thermal oxide film containing a nitrogen component.In this example, if the mixture ratio of the N₂O gas is optimized, asilicon oxynitride film can be obtained through the thermal oxidemethod.

[0119] In this example, there is shown an example in which the gateinsulation film is formed through the thermal oxidation method. However,as another method, the gate insulation film can be formed through thethermal CVD method. Similarly in this case, it is effective thatnitrogen component is contained using N₂O and ammonium.

[0120] (Fifth Embodiment)

[0121] A fifth embodiment of the present invention shows an example inwhich a thin-film transistor is manufactured in a process different fromthat shown in FIGS. 3A to 3E.

[0122]FIGS. 4A to 4E show a manufacturing process in accordance withthis embodiment. First, a crystalline silicon film is formed on a glasssubstrate through a process shown in the first embodiment or the secondembodiment. Then, it is patterned to obtain a state shown in FIG. 4A.

[0123] In the state shown in FIG. 4A, reference numeral 401 denotes aglass substrate; 402, an under film; and 403, an active layer which ismade up of a crystalline silicon film. In this example, it is preferablethat the under layer 402 is formed of a silicon oxynitride film.

[0124] After the state shown in FIG. 4A is obtained, the siliconoxynitride film 404 forming a gate insulation film is formed inthickness of 1000 Å. The film forming method is the plasma CVD methodusing a mixture gas consisting of oxygen, silane and N₂O, or the plasmaCVD method using a mixture gas consisting of TEOS and N₂O.

[0125] It should be noted that a silicon oxide film normally used can beused for the gate insulation film.

[0126] After the silicon oxynitride film 404 that functions as the gateinsulation film has been formed, an aluminum film (not shown) which willfunction as a gate electrode later is formed through the sputteringmethod. 0.2 wt % of scandium is contained in the aluminum film.

[0127] After the formation of the aluminum film, a dense anodic oxidefilm not shown is formed. The anodic oxide film is formed using anethylene glycol solution containing 3% of tartaric acid as anelectrolyte solution. That is, the anodic oxidization is conducted withthe aluminum film as an anode and platinum as a cathode in theelectrolyte solution, to thereby form the dense anodic oxide film on thesurface of the aluminum film.

[0128] The thickness of the dense anodic oxide film not shown is set toabout 100 Å. The anodic oxide film serves to improve the adhesion to aresist mask which will be formed later.

[0129] It should be noted that the thickness of the anodic oxide filmcan be controlled by a supply voltage when anodic oxidizing.

[0130] Thereafter, a resist mask 405 is formed. Then, an aluminum filmis patterned in a pattern indicated by reference numeral 406.

[0131] In this situation, anodic oxidization is again conducted. In thisexample, an oxalic acid aqueous solution of 3% is used as theelectrolyte solution. Anodic oxidization is conducted with the pattern406 of aluminum as the anode in the electrolyte solution, to therebyform a porous anodic oxide film indicated by reference numeral 407.

[0132] In this process, because the resist mask 405 high in adhesionexists in the upper portion, an anodic oxide film 407 is selectivelyformed on the side surfaces of the aluminum pattern 406.

[0133] The anodic oxide film 407 can grow up to several μm in thickness.In this example, its thickness is set to 6000 Å. It should be noted thatthe growth distance can be controlled by anodic oxidation period.

[0134] In this way, a state shown in FIG. 4B is obtained. Then, a denseanodic oxide film is again formed. In other words, using theabove-mentioned ethylene glycol solution containing 3% of tartaric acidas an electrolyte solution, anodic oxidization is again conducted. As aresult, because the electrolyte solution enters in the porous anodicoxide film 407, a dense anodic oxide film as indicated by referencenumeral 408 is formed (FIG. 4C).

[0135] In the state shown in FIG. 4C, the implantation of impurity ionsis first conducted. This process may be conducted after the removal ofthe resist mask 405.

[0136] A source region 409 and a drain region 411 are formed through theimplantation of the impurity ions. Also, no impurity ions are implantedin a region 410.

[0137] Subsequently, the porous anodic oxide film 407 is removed by amixture acid consisting of acetic acid, nitric acid and phosphoric acid.In this way, a state shown in FIG. 4D is obtained.

[0138] After the state shown in FIG. 4D is obtained, the implantation ofimpurity ions is again conducted. The impurity ions are implanted underthe condition of the light doping from the condition of the initialimpurity ion implantation.

[0139] In this process, light doped regions 412 and 413 are formed, andthen a channel formation region indicated by reference numeral 414 isformed (FIG. 4D).

[0140] Thereafter, a laser beam or an intense light is irradiatedthereon, to thereby activate a region in which the impurity ions havebeen implanted. In this way, a source region 409, a channel formationregion 410, a drain region 411, and low-density impurity regions 412 and413 are formed in a self-alignment manner.

[0141] In this example, what is indicated by reference numeral 413 is aregion which is called “LDD (light doped drain) (FIG. 4D).

[0142] Thereafter, a silicon oxide film, a silicon nitride film or alaminate film thereof is formed as an interlayer insulation film 415.The interlayer insulation film 415 is constituted by a layer made of aresin material on the silicon oxide film or the silicon nitride film.

[0143] Then, contact holes are defined to form a source electrode 416and a drain electrode 417. In this way, a thin-film transistor shown inFIG. 4E is completed.

[0144] (Sixth Embodiment)

[0145] A sixth embodiment of the present invention relates to an examplein which an n-channel type thin-film transistor and a p-channel typethin-film transistor are of a complementary type.

[0146] The structure of this embodiment can be used, for example, for avariety of thin-film integrated circuits which are integrated on aninsulation surface. Also, it can be used, for example, for a peripheraldrive circuit of an active matrix liquid-crystal display unit.

[0147] First, a silicon oxide film or a silicon oxynitride film areformed on a glass substrate 501 as an under layer 502 as shown in FIG.5A. Preferably, the silicon oxynitride film is used.

[0148] Further, an amorphous silicon film not shown is formed throughthe plasma CVD method or the low pressure thermal CVD method. Further,the amorphous silicon film is formed into a crystalline silicon filmthrough the method described in the first embodiment or the secondembodiment.

[0149] Then, a crystalline silicon film thus obtained is patterned toobtain active layers 503 and 504. In this manner, a state shown in FIG.5A is obtained.

[0150] Further, a silicon oxynitride film 505 that forms a gateinsulation film is formed. In this process, if quartz is used for asubstrate, it is preferable to use the above-described thermal oxidationmethod (FIG. 5A).

[0151] An aluminum film (not shown) for constituting a gate electrodelater is formed in thickness of 4000 Å. An anodizable metal (forexample, tantalum) can be used except for the aluminum film.

[0152] After the formation of the aluminum film, a very-thin denseanodic oxide film is formed on the aluminum film through theabove-mentioned method.

[0153] Subsequently, a resist mask not shown is arranged on the aluminumfilm, and the aluminum film is patterned. Then, anodic oxidization isconducted with the aluminum pattern thus obtained as an anode, to formporous anodic oxide films 508 and 509. The thickness of the porousanodic oxide films 508 and 509 is set to 5000 Å.

[0154] Further, anodic oxidization is again conducted on the conditionthat a dense anodic oxide film is formed, to form dense anodic films 510and 511 thereby. The thickness of the anodic oxide films 510 and 511 isset to 800 Å. In this way, a state shown in FIG. 5B is obtained.

[0155] Furthermore, the exposed silicon oxide film 505 is removed by dryetching to obtain gate insulation films 512 and 513 as shown in FIG. 5C.

[0156] After the formation shown in FIG. 5C is obtained, the porousanodic oxide films 508 and 509 are removed by a mixture acid consistingof acetic acid, nitric acid and phosphoric acid. In this way, a stateshown in FIG. 5D is obtained.

[0157] In this situation, the resist mask is alternately disposed insuch a manner that P ions are implanted in the left-sided thin-filmtransistor whereas B ions are implanted in the right-sided thin-filmtransistor.

[0158] A source region 514 and a drain region 517 each having n-typewith a high concentration are formed in a self-alignment manner.

[0159] Also, a region 515 having weak n-type where P ions are doped at alow density is formed simultaneously.

[0160] The reason why the region having the weak n-type indicated byreference numeral 515 is formed is that the remaining gate insulationfilm 512 exists. In other words, the P ions that have transmitted thegate insulation film 512 is partially shielded by the gate insulationfilm 512.

[0161] Also, with the same principle, a source region 521 and a drainregion 518 each having a strong p-type are formed in a self-alignmentmanner. Also, a low-density impurity region 520 is formedsimultaneously. Furthermore, a channel formation region 519 is formedsimultaneously.

[0162] It should be noted that in the case where the dense anodic oxidefilms 510 and 511 are thickened to the degree of 2000 Å, offset gateregions can be formed in contact with the channel formation regions 516and 519 by virtue of the thickness.

[0163] In this embodiment, since the dense anodic oxide films 510 and511 are thinned to the thickness of 1000 Å or less, the existence ofthose films 510 and 511 can be ignored.

[0164] Then, a laser beam or an intense light is irradiated thereon toanneal a region in which the impurity ions have been implanted.

[0165] Thereafter, as shown in FIG. 5E, a silicon nitride film 522 and asilicon oxide film 523 are formed as an interlayer insulation film asshown in FIG. 5E. The thickness of the respective films 522 and 523 isset to 1000 Å. It should be noted that the silicon oxide film 523 maynot be formed.

[0166] In this example, the thin-film transistor is covered with thesilicon nitride film 522. Since the silicon nitride film is dense andhas an excellent interface characteristic, this structure enables thereliability of the thin-film transistor to be enhanced.

[0167] Further, an interlayer insulation film 524 made of a resinmaterial is formed through the spin coating method. In this example, thethickness of the interlayer insulation film 524 is set to 1 μm at theminimum (FIG. 5E).

[0168] Then, contact holes are defined to form a source electrode 525and a drain electrode 526 of the left-sided n-channel type thin-filmtransistor. Also, a source electrode 527 and a drain electrode 526 ofthe right-sided thin-film transistor are formed. In this example, thedrain electrode 526 is commonly arranged.

[0169] In the above manner, the thin-film transistor circuit having acomplementary type CMOS structure can be structured.

[0170] In the structure of this embodiment, the thin-film transistor iscovered with a nitride film and also with a resin material. Thisstructure enables the durability to be enhanced which makes the entranceof movable ions and moisture hard.

[0171] (Seventh Embodiment)

[0172] A seventh embodiment of the present invention relates to astructure in which a laser beam is further irradiated on the crystallinesilicon film obtained by the first embodiment or the second embodiment,to thereby form a region which is a mono-crystal or a substantiallymonocrystal.

[0173] First, a crystalline silicon film is obtained using the action ofnickel elements as described in the first embodiment. Then, an excimerlaser (For example, KrF excimer laser) is irradiated on the film tofurther promote the crystallinity.

[0174] The film whose crystallization has been greatly promoted throughthe above method has a mono-crystal like region which is 3×10¹⁷ cm⁻³ orless in electronic spin density which is measured through ESR, and3×10¹⁷ cm⁻³ or less in nickel element density as the minimum valuemeasured through SIMS.

[0175] The grain boundary does not substantially exist in that region,and a high electric characteristic comparable to the mono-crystalsilicon wafer can be obtained.

[0176] Also, the mono-crystal like region contains 5 atoms % or less to1×10¹⁵ cm⁻³ of hydrogen. The value is proved from measurement throughSIMS (secondary ion mass spectrometry).

[0177] With the manufacturing of the thin-film transistor using theregion which is a mono-crystal or a substantially mono-crystal, thecharacteristics comparable to the MOS type transistor manufactured usingthe mono-crystal wafer can be obtained.

[0178] (Eighth Embodiment)

[0179] An eighth embodiment of the present invention exhibits an examplein which a gate insulation film is formed through the thermal CVD methodin a process of manufacturing the thin-film transistor as shown in FIGS.3 to 5. In the case of forming the gate insulation film through thermalCVD method, since heating at a high temperature is required, it isdesirable to use quartz as a substrate.

[0180] In this example, an example is shown in which the gate insulationfilm is formed through the low pressure thermal CVD method at 850° C.,using oxygen gas containing 3% of HCl in volume ratio. The gateinsulation film obtained in the above method can make it difficult tochange the electric characteristic by the entrance of the metal elementsthat exist in the active layer.

[0181] (Ninth Embodiment)

[0182] A ninth embodiment of the present invention exhibits an examplein which nickel elements are introduced directly in the surface of theunder layer during a process shown in the first embodiment. In thiscase, the nickel elements are held in contact with the lower surface ofthe amorphous silicon film.

[0183] As was described above, the present invention can provide atechnique of reducing the concentration of the metal elements in thecrystalline silicon film obtained using the metal elements that promotethe crystallization of silicon.

[0184] Also, the present invention can obtain a thin-film semiconductordevice higher in reliability and excellent in performance.

[0185] The foregoing description of a preferred embodiment of theinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed, and modifications andvariations are possible in light of the above teachings or may beacquired from practice of the invention. The embodiment was chosen anddescribed in order to explain the principles of the invention and itspractical application to enable one skilled in the art to utilize theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto, and theirequivalents.

APPENDIX B

[0186] Pending Applications which Disclose Nickel and Two AnnealingSteps Ser. No. Filing Date 08/255,701  6/07/94 08/496,085  6/28/9508/528,407  9/14/95 08/544,004 10/17/95 08/562,274 11/22/95 08/566,08312/01/95 08/568,792 12/07/95 08/572,008 12/14/95 08/590,325  1/23/9608/590,417  1/24/96 08/620,759  3/18/96 08/630,628  4/10/96 08/636,819 4/23/96 08/685,789  7/24/96 08/688,228  7/29/96 08/709,111  9/06/9608/715,770  9/19/96 08/718,895  9/24/96 08/728,506 10/09/96 08/768,56312/18/96 08/807,737  2/27/97 08/839,940  4/18/97 08/861,001  5/21/9708/863,272  5/27/97 08/877,306  6/17/97 08/893,361  7/15/97 08/897,359 7/21/97 08/897,363  7/21/97 08/905,715  8/04/97 08/968,480 11/12/9708/975,918 11/21/97 08/977,944 11/24/97 09/033,156  3/02/98

APPENDIX C

[0187] Pending Applications which Disclose Nickel and Gettering Ser. No.Filing Date 08/496,085  6/28/95 08/572,008 12/14/95 08/718,395  9/24/9608/728,506 10/09/96 08/721,526  9/26/96 08/768,563 12/18/96 08/769,11412/18/96 08/785,485  1/17/97 08/768,535 12/18/96 08/839,941  4/18/9708/861,001  5/21/97 08/893,361  7/15/97 08/907,182  8/06/97 08/914,573 8/19/97

APPENDIX D

[0188] Pending Applications which Disclose Nickel and Monodomain Ser.No. Filing Date 08/520,079  8/28/95 08/528,407  9/14/95 08/604,547 2/21/96 08/657,801  5/31/96 08/769,113 12/18/96 08/865,047  5/29/9709/026,049  2/19/98

What is claimed is:
 1. A method of fabricating a semiconductor device,said method comprising the steps of: forming an amorphous semiconductorfilm on an insulating surface; introducing a metal material beingcapable of promoting crystallization of the amorphous semiconductorfilm; performing a first heat treatment to crystallize the amorphoussemiconductor film at a first temperature; performing a second heattreatment at a second temperature higher than the first temperature inan atmosphere comprising argon, wherein the second temperature is in arange of 450-1050° C., wherein the crystallized semiconductor film afterthe second heat treatment includes the metal material at a concentrationin a range of 3×10¹⁷ cm⁻³ or less.
 2. A method according to claim 1 ,wherein the crystallized semiconductor film after the second heattreatment has a spin density in a range of 3×10¹⁷ cm⁻³ or less.
 3. Amethod according to claim 1 , wherein the atmosphere in the second heattreatment further comprises a halogen element including at least amaterial selected from the group consisting of HCl, HF, HBr, Cl₂, F_(2,)and Br₂.
 4. A method according to claim 1 , wherein the metal materialis one selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au.
 5. Amethod according to claim 1 , wherein the semiconductor device is oneselected from the group consisting of a liquid crystal display device,an EL display device, and a thin film integrated circuit.
 6. A method offabricating a semiconductor device, said method comprising the steps of:forming an amorphous semiconductor film on an insulating surface;introducing a metal material being capable of promoting crystallizationof the amorphous semiconductor film; performing a first heat treatmentto crystallize the amorphous semiconductor film at a first temperature;performing a second heat treatment at a second temperature higher thanthe first temperature in an atmosphere comprising argon; irradiating thecrystallized semiconductor film with a light after the second heattreatment, wherein the second temperature is in a range of 450-1050° C.,wherein the crystallized semiconductor film after the second heattreatment includes the metal material at a concentration in a range of3×10¹⁷ cm⁻³ or less.
 7. A method according to claim 6 , wherein thecrystallized semiconductor film after the second heat treatment has aspin density in a range of 3×10¹⁷ cm⁻³ or less.
 8. A method according toclaim 6 , wherein the atmosphere in the second heat treatment furthercomprises a halogen element including at least a material selected fromthe group consisting of HCl, HF, HBr, Cl₂, F₂, and Br₂.
 9. A methodaccording to claim 6 , wherein the metal material is one selected fromFe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au.
 10. A method according toclaim 6 , wherein the semiconductor device is one selected from thegroup consisting of a liquid crystal display device, an EL displaydevice, and a thin film integrated circuit.
 11. A method according toclaim 6 , wherein the light is a laser light.